Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

803
FXUS63 KLOT 292019
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
219 PM CST Sat Nov 29 2025

.KEY MESSAGES...

- Periods of moderate to heavy snow will continue into this
  evening producing hazardous travel conditions. The worst
  conditions are ongoing and will persist into this evening, but
  snowfall rates will ease sharply after 8 PM.

- Accumulating snow to impact the Monday afternoon and evening
  commute and result in slick travel conditions.

- Well below normal temperatures will persist through next week.

&&

.DISCUSSION...
Issued at 219 PM CST Sat Nov 29 2025

Through Monday:

Large scale ascent is peaking across the region with our storm
system in full swing at this hour. Persistent, broad UVVs on
the order of 10-15 ubar/second through a 4-6 kft thick DGZ near
and north of I-80 has really helped improve snowflake quality
and resultant SLRs since noon, and this will continue through
the rest of the day, supporting snowfall rates around one half
to, intermittently, one inch per hour.

A notably more convective look to the satellite and radar has
recently taken place across central Illinois where 500-600 mb
lapse rates are steepening ahead of the northward-advancing
dryslot. This has allowed for the development of some embedded
lightning strikes where large scale forcing and the steepest
lapse rates intersect. As a result, wouldn`t be totally
surprised to see a flash near our far south (southern Ford to
Benton counties) during the 3pm-6pm timeframe, along with a
period of briefly very heavy snowfall rates into the 1-2
inch/hour range in that same time window. Latest trends and
guidance suggest the main potential area for these higher rates
will set up in the vicinity of a Gibson City to Paxton line, but
this will be a short window.

The system dryslot will impinge quickly on our locales south of
the Kankakee River Valley through this evening. This will
gradually result in the loss of cloud ice and will transition
lingering precipitation to very poor-quality snow, if not even
flipping things entirely to drizzle late this evening and into
the early overnight. Temperatures will be slowly warming to at
to just above freezing as this occurs, limiting the potential
for any icing impacts. Some additional light snow will be
possible as the low departs very early Sunday morning.

Farther to the north, it looks like we should hold onto just
enough saturation colder than about -10 C that things should
stay all snow north of about I-80. Here, snowfall rates will
diminish through the evening, with just another 2-3 inches of
snow expected overnight.

West to northwesterly winds will steadily increase overnight as
the surface low pulls away, and some gusts could possibly push
40 mph south of I-80. With the warming temperatures, not sure
this will be enough to worsen any blowing snow threat, so
continued to leave this out of the gridded forecast but do
continue a mention west of the Fox Valley Sunday.

Continue to see a signal for one last batch of snow Sunday
morning in association with a trough axis that will push south
out of Wisconsin after 5-6 AM. This feature looks to be pretty
progressive, so will limit residence time, but this could end up
squeezing another quick inch or two of snow near and north of
about I-90 before precip shuts off by mid-late morning. Some
modest lake effect could persist across parts of NE Porter
county through mid afternoon, but the flow largely looks to
shift westerly enough to push the main focus east of our region.
Will continue to keep an eye on this, but at this time, no
plans for headline extensions.

Carlaw


Monday Night through Saturday:

Focus will be on a quick hitting snow event for Monday afternoon
and evening. This system is still developing off the Pacific NW
and dig into the Great Basin and then to the central Rockies by
early Monday. Model guidance depicts additional shortwave
forcing emanating out of the Canadian prairies in a largely
positive to neutrally tilted trough. The degree to which this
northern energy strengthens will play a role to the degree of
impacts from the snow in this event, particularly for areas
north of I-80. The left exit region of an increasing upper jet
will promote a decent area of lift, which will allow an area of
snow to expand across most of the area Monday afternoon. Any
strengthening frontogenetical circulation, albeit transient,
could also translate to higher impacts away from the currently
favored region for elevated snowfall totals which is along and
southeast of I-55, where the low level mass response will be
focused.

Probability matched mean QPF is consistent with the ensemble
envelope of 0.1 to 0.2 inches of QPF, highest southeast, with
less than 0.1" northwest of the Chicago area. This would
translate to a light snowfall toward Rockford to 3" along and
southeast of I-57. While forcing is modest, an increasing
dendritic growth zone could promote a bit fluffier snow than
this past weekend. There are certainly some details to be worked
out here, but a quick hitting impactful snowfall seems on tap
for the Monday afternoon and evening commute where many will be
back at work following the holiday.

KMD

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1144 AM CST Sat Nov 29 2025

18z TAF Forecast concerns:

-Moderate to occasionally heavy snow this afternoon into the
early evening - we are entering the period of peak impacts.

-LIFR visibility with occasional VLIFR (temporary 1/4SM at
 times) in heavier bands

-Increasingly gusty southeast winds mid to late afternoon

Snowfall will hit its peak intensity this afternoon, thus expect
prevailing LIFR conditions with visibilities in the 3/4SM to
1/2SM range in many locations. 1/4SM visibility will mix in from
time to time as snowfall rates ramp up to near 1" per hour this
afternoon. There is a little hole on radar well southwest of
the terminals, but expect that to rapidly fill back in, and we
will need to consider prevailing 1/2SM visibility for all the
terminals. Winds have been slow to respond but will gusts into
the lower 20s (or even mid 20s) later this afternoon and early
evening.

There will be a secondary surge of snowfall, with some rain
mixing in from southwest to northeast through the evening. We
will hold snow at most of the terminals, maybe with the
rain/drizzle mixing in at KGYY. Even as visibility may inch up
mid to late evening, ceilings will fall as low pressure will
move overhead.

Winds will quickly turn around to the WNW overnight into early
Sunday. Expect another batch of snow showers tomorrow morning
before turning to flurries and ending. Gusty WNW winds will
continue (to 25 kt) through the day with MVFR ceilings
returning.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Warning until 6 AM CST Sunday for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-
     ILZ107-ILZ108.

     Winter Storm Warning until midnight CST tonight for ILZ033-
     ILZ039.

IN...Winter Storm Warning until 6 AM CST Sunday for INZ001-INZ002.

     Winter Storm Warning until midnight CST /1 AM EST/ tonight for
     INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 10 PM CST Sunday for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CST Monday for the IN
     nearshore waters.

&&

$$

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